This invention relates to a feature extraction system to detect a required feature from certain signals, and more particularly, to a feature extraction circuit applied to a pattern recognition system.
Techniques for extracting required feature from certain signals are utilized in various field such as a pattern recognition, the examination of manufactured products, measuring systems and automatic control systems, in which a feature extraction circuit is required to operate in quick response to certain signals. In other words, signals output from certain systems such as a pattern recognition system and a temperature measuring system are generally changed when parameters, such as a position, a temperature, a voltage and a time, with respect to the systems vary. In this case, it is important to detect the required feature from the certain signals and to record the values of the parameters corresponding thereto at that time, in order to evaluate the manufactured products and the results of the meansurements, and to control other systems. It is well known that analog memory circuits including capacitar memories are generally used in order to store the required feature and the values of the parameters. The capacitor memories, however, must be small in the time constant thereof to operate in high response to the signals so that it cannot maintain a necessary value for a predetermined period of time since the contents of the capacitor memories are decayed fast. On the contrary, if the time constant of the capacitor memory is made large in order to maintain the necessary value supplied thereto for a predetermined period of time, it cannot be operated in quick response to the signals. In order to resolve the above disadvantages, digital memory circuits may be utilized. In this case, an analog-digital converter is needed in order to convert the analog signals supplied to the memory circuit into the digital signals. The high speed analog-digital converter, however, is required which the period of the repetition is very short and it is high cost. Further, the analog-digital converter applied to the above systems which is required to operate in high speed response to the signals may not be realized even by a conventional high speed analog-digital converter.